1. Field of the Invention
The present invention relates generally to power hand tools, and more particularly, to a power hand tool capable of adjusting torsion and impacting a workpiece.
2. Description of the Related Art
A conventional power impact wrench is primarily composed of an electric motor, a transmission gear set, and an impact device. The transmission gear set is to decelerate the rotary motion of an output shaft of the electric motor down to a predetermined rotary speed and then to output it via the output shaft. The impact device is to apply a rapid discontinuous impact having the same rotary direction as the output shaft does to the output shaft so as to enable the output shaft to overcome the resistance and to keep working.
A conventional power screwdriver is primarily composed of an electric motor, a transmission gear set, and a torsion regulator. The transmission gear set is to decelerate the rotary motion of the output shaft of the electric motor down to a predetermined rotary speed and then to output it. The torsion regulator is to adjust the maximum torsion outputted by power hand tool to avoid damage to a workpiece.
The above-mentioned impact device and torsion regulator are applicable to users' needs to the contrary separately because these two devices generally do not exist in the same power hand tool. However, under few special circumstances, the two devices are needed at the same time. For example, when the user operates a power wrench to dismantle a tire from a car, to overcome the obstacle resulted from rusty bolts or other causes, the power wrench needs the impact device; when the user installs the tire onto the car, to prevent overgreat torsion output of the power hand tool from damage to the bolts provided for fastening the tire onto the car, the power hand tool needs the torsion regulator. However, if the two devices are combined into the same power hand tool, the number of elements and the size of the power hand tool will be inevitably increased to be defective.